On Fri 25-02-22 00:50:18, John Hubbard wrote: > Hi, > > Summary: > > This puts some prerequisites in place, including a CONFIG parameter, > making it possible to start converting and testing the Direct IO part of > each filesystem, from get_user_pages_fast(), to pin_user_pages_fast(). > > It will take "a few" kernel releases to get the whole thing done. > > Details: > > As part of fixing the "get_user_pages() + file-backed memory" problem > [1], and to support various COW-related fixes as well [2], we need to > convert the Direct IO code from get_user_pages_fast(), to > pin_user_pages_fast(). Because pin_user_pages*() calls require a > corresponding call to unpin_user_page(), the conversion is more > elaborate than just substitution. > > Further complicating the conversion, the block/bio layers get their > Direct IO pages via iov_iter_get_pages() and iov_iter_get_pages_alloc(), > each of which has a large number of callers. All of those callers need > to be audited and changed so that they call unpin_user_page(), rather > than put_page(). > > After quite some time exploring and consulting with people as well, it > is clear that this cannot be done in just one patchset. That's because, > not only is this large and time-consuming (for example, Chaitanya > Kulkarni's first reaction, after looking into the details, was, "convert > the remaining filesystems to use iomap, *then* convert to FOLL_PIN..."), > but it is also spread across many filesystems. With having modified fs/direct-io.c and fs/iomap/direct-io.c which filesystems do you know are missing conversion? Or is it that you just want to make sure with audit everything is fine? The only fs I could find unconverted by your changes is ceph. Am I missing something? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
